The present invention relates to a multi-high rolling mill whose sections above and below a rolled material have different numbers of rolls and, more particularly, to a five-high rolling mill, a multi-high rolling mill, and a skinpass rolling mill which are suitable for skinpass rolling or rolling of aluminum.
In general, as a rolling mill of a small rolling reduction and a small rolling force, e.g., a skinpass rolling mill, there has conventionally been often employed a four-high rolling mill which includes upper and lower work rolls provided with bending devices and upper and lower backup rolls supporting these work rolls, as disclosed in Japanese Patent Unexamined Publication No. 48-22344.
However, such a four-high rolling mill does not have a sufficient ability in shape control, and insufficiency of this ability is compensated with various work rolls provided with different crowns. That is why a six-high rolling mill which is superior in the shape control ability has been suggested and applied to practical use (see Japanese Patent Examined Publication No. 57-55484). This six-high rolling mill is arranged in such a manner that upper and lower intermediate rolls are disposed between upper and lower work rolls of the same diameter and upper and lower backup rolls of the same diameter, respectively, and that roll bending devices are installed on the upper and lower work rolls and the upper and lower intermediate rolls, both sets of these bending devices being capable of providing a great ability in the shape control. In the case of skinpass rolling with a small rolling reduction, this six-high rolling mill causes portions of the side ends of a rolling stock to remain non-rolled so that edge wrinkles are formed on the side ends of the rolling stock, thereby resulting in a problem that formation of such edge wrinkles cannot be adequately prevented.
A conventional multi-high rolling mill whose sections above and below a rolling stock have different numbers of rolls or a conventional five-high rolling mill in particular is disclosed in each of Japanese Patent Examined Publication Nos. 60-48242 and 62-46245. Such a five-high rolling mill includes upper and lower work rolls of different diameters, with the upper work roll being a roll of the smaller diameter, and thus, a large rolling reduction can be obtained from a small rolling force. Further, bending devices are installed on both the intermediate roll and the lower work roll of the larger diameter so as to cause the five-high rolling mill to exhibit its ability in controlling a sheet crown. Hence it is possible to control a simply curved (concaved or convex) crown of the rolling stock in its entire width, decrease the rolling force, and enhance the effect of the benders as a result.
On the contrary, in case of i) a rolling operation with both the rolling reduction and the rolling force having small values, ii) a rolling operation which requires an excellent ability in the sheet surface control enabling composite shape control, and iii) a rolling operation which requires prevention of the edge wrinkles, for example, in case of skinpass rolling, rough-surface dull rolls, that is, work rolls in the above-mentioned five-high rolling mill including the upper and lower work rolls of different diameters are extremely shortened in life, and the rolled material is apt to be unfavorably warped. Besides, if the work rolls have small diameters, another problem is caused in that a cross buckle or a folding is apt to be generated during the rolling operation.
A five-high rolling mill including an intermediate roll which has the same drum length as the width of the rolled strip sheet, in which upper and lower work rolls of the same diameter are provided with bending devices, is disclosed in each of Japanese Patent Unexamined Publication No. 54-39349 and Japanese Patent Examined Publication No. 53-34789.
In the use of such five-high rolling mills, it is necessary to replace the intermediate roll with a new one every time the sheet width of the rolled strip sheet is changed, and the rolling operation must be stopped on each such occasion, so that the productivity of the rolling mill will be lowered to a great extent, and the rolling mill will fail to be practical in use. Especially in the case of a skinpass rolling mill installed in a continuous annealing line, since a rolling stock of different widths are continuously supplied thereto, the above-mentioned five-high rolling mill is quite unlikely to be applied to practical use.
Further, five-high rolling mills in which upper and lower work rolls are of the same diameter and these upper and lower work rolls and an intermediate roll of a diameter smaller than that of the work rolls are respectively provided with bending devices as disclosed in Japanese Patent Unexamined Publication No. 56-151103. However, the intermediate roll of such a five-high rolling mill which has a small diameter and the same drum length as that of the backup roll and the work roll, is in contact with the backup roll and the work roll over its entire length, and therefore, the control characteristic of the intermediate roll becomes similar to that of the upper work roll, thereby resulting in a problem that it is basically impossible to accomplish either the composite shape control or the control for prevention of the edge wrinkles.
Although the conventional rolling mills described above are all intended to improve the abilities in shape correction, they cannot satisfactorily perform the skinpass rolling operation in which the rolling reduction and the rolling force are both small and it is necessary to obtain an excellent quality of the surface. More particularly, examples of characteristics of the skinpass rolling operation can be expressed as follows:
i) The rolling reduction is not more than several percent, and the rolling force is not more than half the force of normal cold rolling. PA1 ii) A rough-surface dull roll is often used as a work roll so that the surface of the product will be pear-skinned. PA1 iii) When the side end portions of the stock remain non-rolled, irregularities (edge wrinkles) of the surface are formed thereon due to the stretcher strain, and this is because the rolled stock has been annealed in advance. PA1 iv) Since the stock after the skinpass rolling often becomes a finished product as it is, the product is required to have an excellent surface quality. PA1 1) Work rolls are practically of the same diameter and also of a relatively large diameter. PA1 2) In order to perform composite shape control for providing excellent surface quality, two kinds of control means of different control characteristics are necessary. PA1 3) Third control means other than those means for the composite shape control are required for reducing the edge wrinkles of the strip sheet.
Referring to these characteristics, requirements of a skinpass rolling mill will be reviewed.
First, as for the diameters of work rolls, the rolls are required to have relatively large diameters in order to prevent the cross buckle or folding in the skinpass rolling operation. Also, it is desirable for upper and lower work rolls to have the same diameter (practically the same diameter) in terms of lives of dullness of the work rolls and prevention of warping of a strip sheet after the skinpass rolling process.
As for the shape control of the rolling material to obtain a strip sheet of excellent surface quality, it is necessary for the rolling mill to have an ability in composite shape control for correcting both edge wrinkling and center buckling.
Lastly, it is very important to reduce the widths of the non-rolled side end portions of the strip sheet where edge wrinkles are formed. Since these portions having edge wrinkles are to be cut off as defective parts in the following process, reduction of the widths of the wrinkled portions serves to improve the yield efficiently.
The characteristics of a rolling mill suitable for the skinpass rolling operation can be summarized as follows:
An object of the present invention is to provide a five-high rolling mill by which material can be rolled into a strip sheet having an excellent surface quality even under the conditions of a small rolling reduction and a small rolling force and also formation of edge wrinkles on the side end portions of the strip sheet can be prevented.
Another object of the present invention is to provide a multi-high rolling mill by which formation of such defects as a cross buckle can be prevented during the rolling operation of a small rolling reduction, the ability in the composite shape control of the rolled material can be fully exercised, and also formation of any edge wrinkles on the side end portions of the strip sheet can be prevented.
A still further object of the present invention is to provide a skinpass rolling mill of a compact structure by which stock can be rolled into a strip sheet having an excellent surface quality and also formation of any edge wrinkles on the side end portions of the strip sheet can be prevented.
A further object of the present invention is to provide a rolling method in the multi-high rolling mill by which the ability of the composite shape control of the rolled material can be fully exhibited during the rolling operation of a small rolling reduction and also formation of any edge wrinkles on the side end portions of the strip sheet can be prevented.
In order to attain the above-stated objects, the present invention provides a five-high rolling mill including an intermediate roll which has a diameter larger than upper and lower work rolls of substantially the same diameter and smaller than upper and lower backup rolls, wherein the intermediate roll is formed to have a larger drum length than the maximum width of a rolled material, first roll bending devices are respectively installed on the roll ends of the upper and lower work rolls, while second roll bending devices are installed on the roll ends of the intermediate roll, and the shape of sheet material rolled through the mill is sensed by a shape detector which provides a signal to a controller for actuating the roll bending devices.
In an aspect of the present invention it is preferable to improve the roll bending effects so as to obtain a strip sheet of a more excellent surface quality by providing that the backup roll directly supporting the intermediate roll is in contact with the intermediate roll over a distance smaller than the drum length of the intermediate roll, or by providing that the backup roll directly supporting the intermediate roll is in contact with the intermediate roll over a distance larger than the minimum width of the rolled material and smaller than the maximum width of the same, or that by providing bending devices of the intermediate roll and bending devices on the work roll supported by the intermediate roll that are at least equipped with an increase bender mechanism, while bending devices of the work roll directly supported by the backup roll are at least equipped with a decrease bender mechanism.
The present invention also provides a multi-high rolling mill including a certain number of supporting rolls and a different number of supporting rolls which support upper and lower work rolls of substantially the same diameter so that sections of the rolling mill above and below a rolled material have sets of the rolls in different numerals. In the rolling mill, roll bending devices are installed on the supporting roll directly supporting the work roll in the roll set of the larger number of the rolls, so as to arrange the upper and lower roll sets to have different control degrees, each indicating an amount of change in a sheet crown of the strip sheet which can be controlled by the roll bending devices, while roll bending devices are installed on the respective work rolls in the upper and lower roll sets, in order to differ the control degrees of the sheet crown which can be controlled by the respective roll bending devices for the upper and lower work rolls, and thus, the supporting roll in the one roll set of the larger number of the rolls, the work roll in the same roll set, and the work roll in the other roll set of the smaller number of the rolls are controlled with the control degrees of values gradually increasing in this order.
Moreover, the present invention provides a skinpass rolling mill including an intermediate roll between one of the upper and lower work rolls of substantially the same and large diameter and the associated one of upper and lower backup rolls, wherein the intermediate roll has a drum length larger than the maximum width of a rolled material and smaller than the drum length of the work roll, and roll bending devices are installed on the roll ends of the intermediate roll, while roll bending devices are respectively installed on the roll ends of the upper and lower work rolls, the roll bending devices of the lower work roll being at least equipped with a decrease bender mechanism.
Furthermore, the present invention provides a rolling method in a multi-high rolling mill including upper and lower work rolls of substantially the same diameter, upper and lower backup rolls respectively supporting these work rolls, and an intermediate roll located between one of the upper and lower work rolls and the associated backup roll. In this rolling method applied to the multi-high rolling mill, roll bending devices installed on the intermediate roll and roll bending devices installed on the work roll in the roll set where this intermediate roll is disposed are all actuated to control a composite crown of a strip sheet over its entire width, and roll bending devices installed on the work roll directly supported by the backup roll are actuated to control the crown of the strip sheet in its side end portions, thereby performing both of the composite shape control of the strip sheet and the control of the widths of the side end portions of the strip sheet which are not to be rolled.